A gesture sensor is a human interface device that enables the detection of physical movement without the user actually touching the device within which the gesture sensor resides. The detected movements can be subsequently used as input commands for the device. In some applications, the device is programmed to recognize distinct non-contact hand motions, such as left to right, right to left, up to down, down to up, in to out, and out to in hand motions. Gesture sensors have found popular use in handheld devices, such as tablet computing devices and smartphones, and other portable devices, such as laptops. Gesture sensors are also being implemented in video game consoles that detect the motion of a video game player.
Many conventional gesture sensor implementations use three or more illumination sources, such as light emitting diodes (LEDs), and a light sensor, such as a photo detector. The illumination sources are turned on and off, or flashed, in succession in order for the sensor to obtain spatial information from reflection of the flashed light. FIG. 1 illustrates a simplified block diagram of a conventional gesture sensor. A photo sensor 4 is positioned proximate LED 1, LED 2, and LED 3. A control circuit 5 is programmed to successively turn on and off the LEDs 1-3 and analyze the resulting measurements sensed by the photo sensor 4. Data sensed by the photo sensor 4 is stored separately for each LED. For example, the sensed data corresponding to each flash of LED 1 is stored in an LED 1 register, the sensed data corresponding to each flash of LED 2 is stored in an LED 2 register, and the sensed data corresponding to each flash of LED 3 is stored in an LED 3 register. The result is a time domain signal for each LED. FIG. 2 illustrates an exemplary method for detecting a moving target using the gesture sensor of FIG. 1. The motion is detected by observing the relative delay between sensed signals from the same-axis LEDs. For example, to detect left to right or right to left motion, the signals sensed by the LEDs 1 and 2 are compared, as shown in FIG. 2. LED 1 is flashed at a different time than LED 2. The LEDs 1 and 2 are positioned in known locations and are turned on and off in a known sequence. When the light from the LEDs strikes a target moving above the LEDs, light is reflected off the moving target back to the photo sensor 4. The sensed reflected light is converted to a voltage signal which is sent to the control circuit 5. The control circuit 5 includes an algorithm that uses the LED positions, the LED firing sequences, and the received sensed data to determine relative movement of the target. The separation in time between flashes of successive LED's is quite small compared to the velocity of the moving target and is therefore negligible when comparing the time domain signals from one LED to another.
FIG. 2 shows the time domain sensed voltage signals for both the case of left to right motion and right to left motion. The curves labeled “Signal from LED 1” show the sensed voltage resulting from repeated flashes of the LED 1. The low portion of each curve indicates the target is not passing over, or near, the LED 1. In other words, the target is not within the “field of view”, or coverage area, of the photo sensor 4 whereby light emitted from the LED 1 can be reflected off the target and onto the photo sensor 4. If the target is not within the field of view of the photo sensor 4 as related to the LED 1, the photo sensor 4 does not sense any reflections of light emitted from LED 1. The high portion of the curve indicates the target is within the field of view related to LED 1, which indicates the target is passing over, or near, the LED 1. The curve labeled “Signal from LED 2” shows the sensed voltage resulting from repeated flashes of the LED 2. LED 1 and LED 2 are alternatively flashed such that while LED 1 is on, LED 2 is off, and vice versa. While the target is positioned within the field of view corresponding to LED 1 but not within the field of view corresponding to LED 2, the sensed voltage related to flashing of LED 1 is high, but the sensed voltage related to flashing of the LED 2 is low. In a simplified sense, this corresponds to a target positioned over, or near, LED 1. While the target is positioned in the middle, between the two LEDs 1 and 2, the photo sensor 4 detects reflected light from flashing of both LED 1 and LED 2 resulting in high sensed voltage levels corresponding to both LED 1 and LED 2. While the target is positioned over, or near, LED2, the sensed voltage related to flashing of LED 2 is high, but the sensed voltage related to flashing of the LED 1 is low. When the target is not positioned over either LED 1 or LED 2 or between LED 1 and LED 2, the photo sensor 4 does not sense reflected light associated with either and the corresponding sensed voltage levels are low.
For left to right motion, the sensed voltage level for “signal from LED 1” goes high before the sensed voltage level for “signal from LED 2”, as shown in the Left to Right Motion signals of FIG. 2. In other words, the voltage versus time curve of “signal from LED 2” is delayed relative to the voltage versus time curve of “signal from LED 1” when the target is moving from left to right.
FIG. 2 also shows the sensed voltage signals for the case of right to left motion. For right to left motion, the sensed voltage level for “signal from LED 2” goes high before the sensed voltage level for “signal from LED 1”, as shown in the Right to Left Motion signals of FIG. 2. In other words, the voltage versus time curve of “signal from LED 1” is delayed relative to the voltage versus time curve of “signal from LED 2” when the target is moving from right to left.
Up and down motion, where up and down are considered to be motion in the y-axis, is similarly determined using LEDs 2 and 3 and the corresponding voltage versus time data. The control circuit 5 receives the sensed voltage from the photo sensor 4 and determines relative target motion in the y-axis in a similar manner as that described above in relation to the x-axis.
A disadvantage of the multiple illumination source configuration is the multiple number of illumination source components that must be integrated within the device. With ever decreasing device size, additional components are undesirable.